Marijuana exposure in vivo and human lymphocyte chromosomes

Mutagenicity, developmental toxicity and carcinogenicity of cannabis

Data on the mutagenicity, developmental toxicity and carcinogenicity of cannabis are reviewed in this article. The available evidence on the possible mutagenic effects of cannabinoids is still inconclusive. There is no consensus on the induction of point mutations, while some experimental results suggest that cannabinoids may cause chromosomal damage. Concerning the developmental effects of cannabis, an increased embryolethality and somatic growth retardation have been observed in animals, as well as changes in motor behaviour, after perinatal exposure to cannabinoids. An elevated risk for infertility has been suggested for women smoking marijuana. On the other hand, intrauterine exposure to cannabinoids may be followed by changes of behaviour later in childhood. Finally, the experimental work concerning the possible carcinogenic action of cannabinoids has shown that cannabis acts as a tumour promotor in animals. Epidemiological studies have incriminated cannabis smoking for the development of head and neck carcinomas and for carcinomas of the respiratory tract in humans, but several confounding factors have rendered this evidence inconclusive. At least part of the great popularity of cannabis smoking is due to the widespread belief that it is harmless. However, the studies presented in this review show that, despite their low acute toxicity profile, cannabinoids represent several risks in terms of chronic toxicity.

Frequencies of hprt mutant lymphocytes in marijuana-smoking mothers and their newborns

Reports of increases in the prevalence of marijuana smoking, especially among young people, have led to concerns about possible genotoxic effects from marijuana use due to exposure to the mutagenic and carcinogenic agents present in marijuana smoke. Prior studies of the adverse health consequences of marijuana smoking, using disease outcomes, have sometimes been confounded by the fact that most marijuana smokers also smoke tobacco. In the present study, the potential mutagenic effects of marijuana smoking were investigated with a somatic cell mutation assay that detects mutations occurring in vivo in the hprt gene. Subjects were volunteers recruited from a prenatal clinic that performs urine drug screens on all consenting patients. Blood samples were collected from 17 subjects whose drug screens indicated marijuana use, but who did not smoke tobacco or use cocaine or opiates, and 17 non-smokers with negative drug screens. Absence of tobacco use was confirmed by plasma cotinine tests. Cord blood samples were collected from newborns of 5 of the marijuana smokers and 5 non-smokers. Lymphocytes were isolated, cryopreserved, and later thawed and assayed with the autoradiographic hprt assay. The frequency of variant (mutant) lymphocytes (Vf) in the 17 non-smokers (+/- standard error) was 1.93 (+/- 0.17) per million evaluatable cells. The Vf of 17 marijuana smokers was more than three-fold higher, 6.48 (+/- 0.48) x 10(-6), a significant difference, p < 0.001. Cord blood lymphocytes from 5 newborns of non-smokers had a Vf of 0.85 (+/- 0.23) x 10(-6), compared to 2.55 (+/- 0.60) x 10(-6) for 5 newborns of marijuana smokers, significantly higher, p < 0.05. Because of the known association between increases in somatic mutations and the development of malignancies, this study indicates that marijuana smokers may have an elevated risk of cancer. For pregnant marijuana smokers, there is also concern for the possibility of genotoxic effects on the fetus, resulting in heightened risk of birth defects or childhood cancer.

Genetic effects of marijuana

Marijuana and its constitutive cannabinoids--tetrahydrocannabinol (THC), cannabinol (CBN), and cannabidiol (CBD)--markedly affect mammalian cells. Cytogenetic studies have revealed that cannabinoids induce chromosome aberrations in both in vivo and in vitro studies. These aberrations include chromosomal breaks, deletions, translocations, errors in chromosomal segregation, and hypoploidy, and are due to the clastogenic action of cannabinoids or to cannabinoid-induced disruption of mitotic events or both. Conflicting reports of the cytogenetic effects of cannabinoids are partially explained by the different experimental protocols, cell types, and animals used by investigators. Cannabinoids also suppress macromolecular synthesis (DNA, RNA, and protein) as well as reduce the level of histone gene expression. In general these studies show that cannabinoids are detrimental to the health of an individual.

Mutagenicity of marijuana and Transkei tobacco smoke condensates in the Salmonella/microsome assay

Extracts and smoke condensates of marijuana, Transkei home-grown tobacco and also commercial cigarette tobaccos were assayed for their mutagenic activity to Salmonella typhimurium strains TA98, TA100, TA1535, TA1537 and TA1538, both with and without metabolic activation. No mutagenic activity was detected in dichloromethane extracts of marijuana and tobacco per se, but all the smoke condensates exhibited mutagenicity with metabolic activation. The only strain not mutated by any of the pyrolyzates was TA1535. Transkei tobacco pyrolyzate proved to be the most mutagenic, followed by marijuana, pipe and cigarette tobacco. Mutagenicity was positively associated with the nitrogen content of the various products. The potent mutagenic action of marijuana smoke condensate, coupled with a condensate yield of more than 50% higher than that of cigarette and pipe tobacco, indicates a high carcinogenic risk associated with marijuana smoking.

In vitro induction of segregational errors of chromosomes by natural cannabinoids in normal human lymphocytes

It has been shown that segregational errors (SE) of chromosomes can be induced by olivetol and several halogenated inhalation anesthetics. The purpose of this study was to examine the effects of natural cannabinoids - including delta-9-tetrahydrocannabinol (THC), cannabinol (CBN), and cannabidiol (CBD) - on chromosome segregation. Lymphocytes obtained from healthy adult males were incubated with various concentrations of natural cannabinoids for 72 hours. Anaphase preparations were made from these cultures. A statistically significant increase in the incidence of SE of chromosomes was observed in the lymphocytes exposed to THC at a concentration of 3.2 x 10(-6) M, but not to CBN or CBD. A greater incidence of bridge formations, anaphase lags, micronuclei, and unequal segregations in bipolar divisions and multipolar divisions were observed in THC-treated lymphocytes, compared with the controls. However, only anaphase lags and unequal segregations in bipolar divisions reached statistically significant levels. It appears that THC affects the formation of microtubules and spindles and may be considered as a mitotic poison. The value of examining SE as a part of cytogenetic studies on chemical mutagens is emphasized. A description of a classification system of SE developed in our laboratory is also presented. This system can be applied to studies using both normal human lymphocyte cultures and lymphoid cell lines.

Mutagenicity testing of 3 hallucinogens: LSD, psilocybin and delta 9-THC, using the micronucleus test

Using the micronucleus test as a screening method for mutagenic activity, no significant increase in the number of micronuclei was found when LSD, psilocybin or delta 9-THC were administered in 3 logarithmically increasing doses to mice, Azathioiprine (Imuran), given as a positive control, caused a statistically significantt increase in the micronucleated cells.